The present invention broadly relates to stop motions for looms and, in particular, concerns a new and improved construction of an electrical warp thread-monitoring apparatus for a loom.
The warp thread-monitoring apparatus of the present development is of the type comprising a multiplicity and drop wires each carried by a warp thread and current rails which extend over the entire width of the warp threads. In the presence of rupture of a warp thread the current rails can be electrically connected with one another by the related drop wire which has dropped. The current rails are located conjointly in an alternating-current circuit in order to produce a stop or shutdown signal for the loom in the presence of warp thread rupture.
An entire host of requirements are placed upon equipment of this type, which for reasons of safety also must be maintained and which particularly arise by virtue of the varying surounding conditions at the region of the drop wires and the current rails during the weaving operation. Such conditions require, among other things, a spark-free contact to be made between the drop wires and the current rails. Additionally, there is required a positive functioning of the current circuit, and thus, a positive generation of a stop or shutdown signal even in the presence of increasing contamination during operation of the loom. Additionally, there must be prevented faulty functioning due to leakage currents, for instance arising in the presence of increased humidity, and finally, there must be avoided faulty response of the monitoring apparatus due to vibrating (dancing) drop wires.
None of the heretofore known electrical warp thread-monitoring apparatuses is however capable of satisfying all of the aforementioned requirements. In particular, the heretofore known warp thread-monitoring apparatuses are neither capable of preventing spark formation nor faulty operation in the presence of increasing fluff formation and/or increasing air humidity.
Thus, in Swiss Pat. No. 555,914 there has only been proposed connecting into the current circuit of an electrical warp thread-monitoring apparatus a time-delay relay, in order to enable response of the stop motion device at the loom only then when a current pulse of the warp thread-monitoring apparatus lasts beyond a predetermined period of time.
Furthermore, in British Pat. No. 1,054,559 there is taught to the art an arrangement wherein for increasing the contact between the drop wires and the contact rails there is employed a cold cathode tube. The employed circuit responds in the presence of the most brief pulses, as soon as such correspond to the ignition or firing potential. This is disadvantageous in as much as the cold cathode tubes also can be fired in the presence of leakage currents which, in practice, can flow between the contact rails due to the presence of contaminants (formation of snarls or fluff and moisture). Additionally, the circuit can respond in the presence of pulses which are formed due to vibration or dancing of the drop wires.
In British Pat. No. 1,209,728 there is taught a circuit arrangement wherein an integrator stage prevents response of the circuit to short pulses. Here however the response time is influenced so extensively by the transfer resistance at the warp thread monitor-drop wire-contact, which can fluctuate in practice between 0 and 30 Kilohms that there is precluded any positive switching operation.